The present invention relates to a method and device for controlling an automatic transmission particularly mounted on a vehicle having an automatic stop mechanism of an engine.
Recently, vehicles equipped with a mechanism for automatically stopping an engine while waiting for a traffic light, etc. (idle stop mechanism) have been developed and put into practical use in order to reduce environmental loads, such as a fuel consumption. It is proposed that such a vehicle equipped with the automatic engine stop mechanism be provided with a mechanical oil pump using the engine as a drive source and, additionally, a hydraulic pressure supply device such as an electric oil pump or a hydraulic accumulator, in order to supply hydraulic pressure to an automatic transmission. JPH08-014076A discloses one example of such a vehicle.
When the hydraulic pressure is supplied to the automatic transmission by the mechanical oil pump alone, frictional engageable elements of the automatic transmission are disengaged when the engine is automatically stopped, which may cause an engaging shock due to a response delay when restarting the engine. In order to reduce this engaging shock, JPH08-014076A proposes a vehicle provided with a hydraulic pressure supply device in addition to a mechanical oil pump for supplying hydraulic pressure to frictional engageable elements.
In addition, in order to reduce a shock caused in a vehicle in an engine restart, JP2011-208699A proposes a configuration of reducing hydraulic pressure that is supplied from a hydraulic pressure supply device (an electric oil pump or a hydraulic accumulator) to engage frictional engageable elements, while an engine is automatically stopped. In this manner, the shock caused in the vehicle by a torque fluctuation occurring in the engine restart and being transmitted to drive wheels can be reduced.
Although a certain level of the shock caused in the vehicle in the engine restart may be reduced by the configuration proposed in JP2011-208699A, a response delay at the time of an engaging operation of an automatic transmission becomes another problem. That is, according to the configuration proposed in JP2011-208699A, since the hydraulic pressure supplied from the hydraulic pressure supply device is kept low while the engine is automatically stopped, obtaining a suitable engaging force at the engine restart takes time. Therefore, this configuration may cause the response delay at the time of the engaging operation of the automatic transmission in the engine restart.